Formation of silicide coatings on the surface of a TiAl-based alloy and improvement in oxidation resistance

A simple and inexpensive method to modify the surface of a TiAl-based alloy by liquid-phase siliconizing has been proposed. After siliconizing in Al-12.87 wt.% Si melt, the surfaces of the TiAl-based alloy were covered with a layer of silicides, composed of ternary TiAlSi and binary TiSi compounds. The thickness of the silicide coatings increase with siliconizing temperature (T) and siliconizing time (t), in +accordance with the parabolic law, and the parabolic rate constant (k) can be described by k = 2.24 × 10−5exp(−107110/RT) m2/s. The results of the isothermal oxidation test show that the silicide coatings exhibit an excellent oxidation resistance. Some of the siliconizing products, Ti7Al5Si12 and two kinds of TiSi compounds, were still preserved after oxidation at 1173 K for 100 h, and Al4Ti2SiO12, TiO2 and Al2O3 as well as SiO2 were formed at the surface of the siliconized sample, but the continuous TiO2 scale or the loose mixture layer of TiO2 and Al2O3 existing in the bare TiAl alloy was not present in the coatings.